This is the mail system at host plesk.example.com.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.

Emails sent to all other external servers get routed to Spam folder.

Cause

Server IP is blacklisted globally and spam settings on a recipient server are too strict.

Resolution

To get email delivered to recipient@domain.tld, mail.domain.tld spam settings should be adjusted